Typical impulse communications systems make a number of assumptions. For example, many impulse communications systems assume that the impulse power of the signal will exceed the background noise level sufficiently to provide adequate signal-to-noise ratio for operation. Also, many impulse communications systems assume a quiet spectrum in the frequency band of operation. Typically, very little coding of the signal is done in impulse communications systems. The coding that is typically done is usually error detection and correction rather than coding to ensure signal integrity. One example of error detecting and correcting coding is Reed Solomon coding.
It is not always valid to assume either a quite spectrum or that impulse power will always sufficiently exceed background noise level. For example, impulse noise sources can cause a pulse to be detected when no pulse was transmitted in the original signal. Some systems reject noise by using multi-bit symbols and monitoring for pulses when a pulse is expected. If the pulses received match the pulses expected, the multi-bit symbol is considered a valid symbol. However, it is still possible that, in these systems, noise can cause pulses to be detected when expected even though no pulse was transmitted at that time. When this happens a symbol may be considered a valid symbol even though the symbol is the result of noise and not a transmitted data signal.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a communications system which has improved noise immunity.